1. Field of the Invention
This invention relates to a cooling device for a high temperature, high pressure vessel and is applied to a hot isostatic pressurizing equipment (HIP equipment).
2. Description of the Prior Art
Various HIP equipments which make use of involved effects of a high isostatic pressure and a high temperature in a high pressure vessel for pressurizing sintering of powder material of various metals, ceramics and so forth, removal of internal defects of cast articles and sintered articles, diffused junction and so forth are employed in various industrial fields.
Since such a HIP equipment, particularly a high pressure vessel therein, is acted upon by a high internal pressure equal to or higher than 1,000 kgf/cm.sup.2 and also undergoes a high temperature, an inner wall of the vessel at which a highest stress takes place as the pressure rises begins its plastic deformation, and if the region of the plastic deformation increases until the entire vessel is plastically deformed, there is the possibility that the vessel may be broken.
Further, if the temperature in use rises, a creep phenomenon may take place under a fixed pressure, and if the repetition frequency of pressurization increases, there is the possibility that a fatigue failure may take place in the vessel.
Such circumstances as described above must be coped with from a point of view of assurance of safety. To this end, a heat insulating structure, cooling of the vessel and so forth are required for a HIP equipment. Exemplary devices for cooling a vessel are disclosed. for example, in Japanese Patent Publication No. 56-8717. The prior art devices have such a construction as shown in FIGS. 15 and 16.
Referring first to FIG. 15, a HIP equipment includes a high pressure cylinder 110 as a main body. The high pressure cylinder 110 is composed of an inner tube 130 and a sheath 131 formed from a band which surrounds an outer periphery of the inner tube 130 and on which a stress is imposed in advance. A steel plate tube 136 is interposed between the inner tube 130 and the sheath 131, and a large number of rods 133 are placed between the inner tube 130 and the steel plate tube 136 and extend in an axial direction to form an annular layer. Cooling medium is flowed along paths 139 between the steel plate tube 136 and the rods 133 to cool the high pressure cylinder 110 from the outside.
Referring now to FIG. 16, a HIP equipment shown is a modification to the HIP equipment shown in FIG. 15. In the modified HIP equipment, rectangular rods 150 are placed between an inner sheath 131a and an outer sheath 131b each formed from a band such that a cooling water path 151 may be formed between each adjacent ones of the rectangular rods 150 so as to cool a high pressure cylinder 110 similarly from the outside.
Meanwhile, improvement in productivity is also an important subject of a HIP equipment.
In particular, a HIP equipment has a fault that processing for one cycle requires a long period of time.
Thus, improved HIP equipments have been proposed wherein convection flows of gas are made use of in a cooling step after completion of a HIP processing step in order to reduce the cooling time. An exemplary one of such improved HIP equipments is disclosed, for example, in Japanese Utility Model Publication No. 62-24238.
However, the prior art HIP equipments shown in FIGS. 15 and 16 and described hereinabove are disadvantageous in cooling effect and also in that the high pressure cylinder is complicated in structure because the cooling device is provided on the outer periphery of the high pressure cylinder to cool the inside of the high pressure cylinder. Besides, in order for the cooling device to have a high and efficient cooling function, the entire HIP equipment including the high pressure cylinder must be increased in diameter and also in overall size.
Further, use of such large number of axially extending rods 133 requires a very high degree of accuracy in working accuracy of outer faces of the rods 133 and also in assembling accuracy and so forth of the rods 133 and also requires a high production cost in order to allow the rods 133 to be used as components of a high pressure vessel which can stand a high pressure, for example, higher than 500 atmospheres. Besides, after the rods 133 are assembled once, it is difficult to confirm a surface condition of the inner tube 130, sheath 131, inner wall 132, tube outer face 135 and so forth, and maintenance of the cooling device itself is difficult.
Further, since the prior art HIP equipments involve cooling only from the outside of the vessel, even if the technique of the improved HIP equipments described above is combined with the prior art HIP equipments, involved actions of convection flows of gas and cooling of the vessel cannot be exhibited satisfactorily.